Apparatus and method for manufacturing a turbocharger component

ABSTRACT

A method of manufacturing a turbocharger component for an internal combustion engine is disclosed. The method may include introducing a material into a mold, wherein the material includes at least one added alloying element. The method may further include applying a pressure to the material, and solidifying the material by cooling the material at a cooling rate, wherein the solidifying preserves an amount of the at least one added alloying element in solid solution in the material. The method may also include forming precipitates within the material by aging the material at an aging temperature.

TECHNICAL FIELD

The present disclosure relates generally to a turbocharger system, andmore particularly to an apparatus and method for manufacturing aturbocharger component.

BACKGROUND

Internal combustion engines are supplied with a mixture of air and fuelfor subsequent combustion within the engine that generates a mechanicalpower output. To increase the power generated by the combustion process,the engine may be equipped with a turbocharger system including one ormore turbochargers. The turbocharger system can be arranged to useexhaust from the engine to compress air flowing into the engine, therebyforcing more air into a combustion chamber of the engine than couldotherwise be draw in to the combustion chamber. The increased supply ofair can allow for increased fueling, resulting in an increased poweroutput.

An internal combustion engine having a turbocharger system may becomposed of various components such as one or more turbine wheels,compressor wheels, and/or pistons. Turbocharger components have beenconstructed from materials capable of withstanding high temperatures andstresses that can be experienced during engine operation. For example,temperatures of compressed air can reach about 260-300° C. during engineoperation. Such high operating stresses and temperatures may have anadverse effect on engine operation.

In an attempt to endure these high temperatures and stresses,turbocharger components, including compressor wheels, have been made ofa titanium alloy. Titanium compressor wheels, however, may inhibitefficient engine operation due to their weight, and the costs associatedwith manufacturing titanium compressor wheels may be excessive. In lieuof using titanium, compressor wheels may be manufactured from aluminum.Aluminum, however, may not be able to withstand the high temperaturesand stresses imparted on the compressor wheels during engine operation.

U.S. Pat. No. 8,118,556 (“the '556 patent”) describes a compressor wheelfor a turbocharger system. In particular, the '556 patent discloses acompressor wheel formed of an aluminum alloy containing up to 5 weightpercent (wt %) scandium. According to the manufacturing processdescribed in the '556 patent, compressor wheels may be manufactured by anumber of casting methods, such as vortex casting, vacuum casting,centrifugal casting, die casting, and pressure casting. In one example,molten material is pressure cast into a shell mold and solidifies toform a compressor wheel.

While an aluminum-scandium alloy like that disclosed in the '556 patentmay be used to form a compressor wheel, depending on the manufacturingprocess, the compressor wheel may still not be able to sufficientlywithstand high stresses and operating temperatures in the range of about260-300° C. The present disclosure is directed to overcoming one or moreof the these issues and/or other problems.

SUMMARY

In one aspect, a method of manufacturing a turbocharger component for aninternal combustion engine is disclosed. The method may includeintroducing a material into a mold, wherein the material includes atleast one added alloying element. The method may further includeapplying a pressure to the material, and solidifying the material bycooling the material at a cooling rate, wherein the solidifyingpreserves and amount of the at least one added alloying element in solidsolution in the material. The method may also include formingprecipitates within the material by aging the material at an agingtemperature.

In another aspect, a component for a turbocharger of an internalcombustion engine is disclosed. The component may be manufactured by amethod including introducing a material into a mold, wherein thematerial includes at least one added alloying element. The method mayfurther include applying a pressure to the material, and solidifying thematerial by cooling the material at a cooling rate, wherein thesolidifying preserves an amount of the at least one added alloyingelement in solid solution in the material. The method may also includeforming precipitates within the material by aging the material at anaging temperature.

In yet another aspect, a component for an internal combustion engine isdisclosed. The component may include an aluminum-scandium alloy havingnanometer-sized precipitates, and the alloy may include about 0.2 wt %scandium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an internal combustion engine including aturbocharger system according to the present disclosure;

FIG. 2 is a schematic cross-sectional view of a casting apparatus formaking a component of the turbocharger system of FIG. 1; and

FIG. 3 is a magnified schematic view of a portion of a compressor wheelof the turbocharger system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary embodiment of an internal combustionengine 10. Although various internal combustion engines could beprovided, for the purposes of illustration, the engine 10 shown in FIG.1 is a four stroke, compression ignition engine. The engine 10 includesan engine block 12 defining a plurality of combustion chambers orcylinders 14. Although in the exemplary engine 10, six combustionchambers 14 are shown, the engine 10 may include any number ofcombustion chambers 14. The engine 10 also includes an intake manifold16 in communication, for example, fluid communication, with thecombustion chambers 14, such that the intake manifold 16 may be capableof providing air to the engine 10 via an intake conduit 18. An exhaustmanifold 20 may also be in communication, for example, fluidcommunication, with the combustion chambers 14, such that the exhaustmanifold 20 may be capable of expending exhaust gas from the engineblock 12 via an exhaust gas conduit 22.

The engine 10 may also include a turbocharger system 24. Theturbocharger system 24 may be a single stage turbocharger system or amultiple stage turbocharger system, as shown in FIG. 1. In one instance,the turbocharger system 24 may include a first turbocharger 26 and asecond turbocharger 28. Although two turbochargers 26, 28 are shown inFIG. 1, in some instances an engine 10 may include one turbocharger ormore than two turbochargers. The first turbocharger 26 may include acompressor 30 connected to a turbine 32 via a shaft 34. Similarly, thesecond turbocharger 28 may include a compressor 36 connected to aturbine 38 via a shaft 40.

During operation of the internal combustion engine 10, exhaust gasleaving the exhaust manifold 20 passes through the exhaust conduit 22 toturbine wheels 42, 44, causing the turbine wheels 42, 44 to rotate. Therotation of the turbine wheels 42, 44 turns the shafts 34, 40, whichrotate compressor wheels 46, 48, respectively. Ambient air flows throughthe intake conduit 18, and the rotation of the compressor wheels 46, 48compresses the ambient air. In some instances, a multiple stageturbocharger system may include compressor wheels operating in series,as shown in FIG. 1. In other instances, a multiple stage turbochargersystem may include compressor wheels positioned and operating inparallel on a common shaft.

FIG. 2 is a schematic cross-sectional view of a casting apparatus 50,which may be referred to as a pressure casting apparatus 50, for makinga component of a turbocharger. As described in detail in thisdisclosure, the casting apparatus 50 may be arranged to castturbocharger components such as one or more of the turbine wheels 42,44, the compressor wheels 46, 48, piston heads (not shown), cylinderheads (not shown), or a variety of other engine components.

As shown in FIG. 2, the casting apparatus 50 may include a mold 52. Themold 52 may include a cavity 62 defined by an interior mold wall 80 andconfigured to receive a casting material, also referred to as meltstock, during a casting process, as described in detail in thisdisclosure. In some instances, the mold may be referred to as a“retractable mold” made of multiple separable pieces. In otherembodiments, the mold 52 may be constructed as a single piece. Whetherthe mold 52 is retractable or a single piece, the mold 52 may be eitherreusable or disposable. As described herein, the mold 52 shown in FIG. 2is a schematic cross-sectional view of the mold 52, and therefore maynot represent the actual shape of the mold 52 and/or mold cavity 62. Forexample, the mold cavity 62 may have a more complex shape into which thecasting material can flow based on, e.g., the shape of compressor wheelblades.

The casting apparatus 50 may further include a ram 54, which, in someinstances, may be a hydraulic ram. As shown in FIG. 2, the mold 52 mayrest or be secured atop the ram 54. The ram 54 may include a piston 58,plunger, or similar device configured to introduce the casting materialinto the mold cavity 62, as described in this disclosure. The piston 58may be linearly movable within an interior 74 of a cylinder 76 of theram 54. The piston 58 may be movable up to or beyond an upper end 64 ofthe ram 54. The volume of casting material that can be contained withinthe cylinder 76 can be the same or substantially the same as the volumeof the mold cavity 62. In other instances, the volume of castingmaterial that can be contained within the cylinder 76 may be less thanthe volume of the mold cavity 62.

In some instances, the mold 52 and/or the ram 54 may be made from ametal, such as stainless steel. In other instances, the mold 52 and/orthe ram 54 may be constructed of another metal. In yet other examples,the mold 52 and/or ram 54 may be made from a non-metallic material, suchas sand, which may insulate the molten alloy until solidification viathe cooling mold 56 occurs. If the mold 52 and/or the ram 54 areconstructed of a non-metallic material, they may be encased by asupporting mechanism such as a metal housing or fixture. The mold 52 andthe ram 54 may be either made of the same or different materials.

The casting apparatus 50 may also include a cooling mold 56 that mayrest or be secured atop the mold 52. The cooling mold 56 may also bereferred to as a chill mold, a cooling block, a cooling member, or thelike. The cooling mold 56 may include a coolant passage 66 for receivinga coolant and allowing the coolant to flow within the cooling mold 56.In some instances, the coolant passage 66 may extend from a cooling moldinlet 68 to a pair of cooling mold outlets 70, 72. As shown in FIG. 2,the portion of the coolant passage 66 extending directly from the inlet68 may be larger than the portion of the coolant passage 66 extendingdirectly from either outlet 70, 72. In other embodiments, however,dimensions of the coolant passage 66 (e.g., internal width or diameter)may vary, or the coolant passage 66 may have a constant width ordiameter throughout the cooling mold 56. Additionally, although FIG. 2shows a single inlet 68 and two outlets 70, 72, any number of inlets oroutlets may be constructed in the cooling mold 56. The inlet 68 can beconfigured to allow a fluid such as coolant to flow into the coolingmold 56, and each outlet 70, 72 can be configured to allow the fluid toflow out of the cooling mold 56. In some instances, the cooling mold 56may be made of a metal or may be an alloy, such as a copper alloy orsteel.

In some embodiments of the casting apparatus 50, a gasket 60 or similardevice may be disposed between the cooling mold 56 and the mold 52. Thegasket 60 may be also be referred to as an insulation gasket 60, and maybe configured to seal and insulate the casting material within the moldcavity 62 during casting. Due to its position, the gasket 60 mayinsulate the cooling mold 56 from the mold 52, which, as described inmore detail below, may be preheated prior to casting. The gasket 60 maybe annular such that the underside 78 of the cooling mold 56 is exposedto the mold cavity 62. Thus, an annular gasket 60 may be disposedbetween the cooling mold 56 and the mold 52, but not between the coolingmold 56 and the mold cavity 62, such that casting material in the moldcavity 62 may be in contact with the underside 78 of the cooling mold56. In some instances, the contact between the casting material withinthe mold cavity 62 and the cooling mold 56 may be direct physicalcontact and/or thermal contact, as described in more detail below.

FIG. 3 illustrates a magnified schematic view of a portion 82 of one ofthe compressor wheels 46, 48 of FIG. 1. The portion 82 may be a surfaceportion of one of the compressor wheels 46, 48 or a portion in a depthdirection showing various depths of the material forming one of thecompressor wheels 46, 48. The portion 82 includes a number ofprecipitates 84 formed by precipitation occurring after a cooling andsolidification process, described in more detail below.

The process of precipitation may also be referred to as precipitationhardening. Precipitates 84 may be formed in the alloy casting materialduring an aging process. The precipitates 84 may be located within thecast component (e.g. the compressor wheel) and harden the component bypreventing and/or obstructing the movement of irregularities (e.g.dislocations) within the crystal structure of the alloy.

The precipitates 84 may be referred to as nanometer-sized precipitateshaving a distance 300 representing a width or diameter of an individualprecipitate 84. In some instances, the distance 300 may be between about1 and 50 nm. The distance 300 may be substantially the same or varyslightly for each precipitate 84 of the compressor wheel. In someexamples, the distance 300 may differ among the multiple precipitates 84of the compressor wheel due to variations in shape among theprecipitates 84. Although the precipitates 84 are shown in FIG. 3 asbeing circular, the precipitates 84 may actually have various, irregularshapes.

FIG. 3 also shows distances 400 and 500 between precipitates 84.Distance 400 may represent the distance between any one pair ofprecipitates, while distance 500 may represent the distance between anydifferent pair of precipitates. The distances 400 and 500 may representthe distances between any precipitates in the portion 82, or in the anyof the material forming one of the compressor wheels 46, 48. In someinstances, the distances 400 and 500 between two pairs of precipitatesmay be substantially the same, having a value of between about 2 and 40nm. In one exemplary embodiment, the distances 400, 500 may be about 25nm. In other instances, the distances 400 and 500 may differ. When thedistances 400, 500 are substantially the same throughout one of thecompressor wheels 46, 48, the precipitates 84 may be referred to asbeing uniformly distributed throughout the compressor wheels 46, 48.When the distances, such as the distances 400, 500, between precipitates84 vary throughout one of the compressor wheels 46, 48, the precipitates84 may be referred to as being non-uniformly or randomly distributedthroughout the compressor wheels 46, 48.

FIG. 3 shows only a portion 82 of one of the compressor wheels 46, 48,and additional precipitates 84 may be arranged in a similar fashion inother portions or throughout the material forming the entire structureof the compressor wheels 46, 48. Furthermore, the values for thedistances 300, 400, 500 are exemplary only. Distances 300, 400, 500 maybe greater than or less than the values described herein.

An exemplary method of manufacturing a compressor wheel using thecasting apparatus 50 shown in FIG. 2 will now be described. Thechemistry of the casting material, which may also be referred to as meltstock, an alloy, a molten alloy, an alloy material, an alloy castingmaterial, or the like, may include one or more of the following: copper,magnesium, zinc, nickel, iron, scandium, zirconium, titanium, aluminum,manganese, chrome, lithium, and silicon. For example, the alloy mayinclude about 1 to 4 wt % copper, 0 to 3 wt % magnesium, 0 to 7 wt %zinc, 0 to 2 wt % nickel, 0 to 2 wt % iron, at least one of thefollowing: up to about 2 wt % scandium, 0 to 2 wt % zirconium, and 0 to1 wt % titanium, with the balance of the alloy being aluminum. Otheralloy materials may also be used. In some instances, various elementssuch as strontium and sodium may also be used in the casting materialand may be referred to as modifying elements or microstructuremodifiers. The scandium, zirconium, and titanium may each be referred toherein as an added alloying element, added alloying material, addedmaterial, or the like. In one instance, the alloy may be analuminum-scandium alloy including up to about 5 wt % scandium. Inanother instance, an aluminum-scandium alloy may include up to about 2wt % scandium. As used herein, “wt %” indicates a given element'spercentage of the total weight of the alloy. The alloy may be melted andheld at a temperature for a period of time. In one instance, the alloymay be held at about 750° C. for about thirty minutes, at which pointthe temperature may be lowered to about 730° C. before the alloy isready to be introduced into the mold 52.

At a time either before or after the alloy is being melted, or duringthe melting of the alloy, one or more of the mold 52, the ram 54, andthe cooling mold 56 can be prepared for casting. The mold 52 and/or theram 54 may be preheated by one or more heating elements (not shown).Various types of heating elements may be used. For example, the heatingelement may be one or more internal passages formed within the mold 52and/or the ram 54 through which a heated fluid (e.g. oil) may flow. Theinternal passages may have a variety of cross-sections (e.g. circularcross-sections) and may be arranged in any fashion within the mold 52and/or ram 54. For instance, the internal passages may be a plurality oflinear passages extending through the mold 52 and/or ram 54, or theinternal passages may one or more curved or helical passages within themold 52 and/or ram 54. In other examples, the heating element may be aninduction coil or electrical resistive heating element disposed on theoutside of the mold 52 and/or the ram 54. In one instance, the heatingelement may preheat the mold 52 and/or ram 54 to a temperature of about200° C. prior to casting.

To prepare the cooling mold 56 for casting, a coolant can be introducedinto the coolant passage 66 via the inlet 68 to flow in a direction 200towards the outlets 70, 72. In some instances, the inlet 68 may serve asan outlet and the outlets 70, 72 may serve as inlets such that thecoolant flow direction 200 can be reversed.

After the molds 52 and 56 are prepared, pressure casting may begin.Pressure casting may also be referred to as pressurized casting, and mayencompass processes such as squeeze casting. To begin casting thecompressor wheel, the piston 58 may advance within the cylinder 76toward the mold cavity 62 in a direction 100 to pressurize the castingmaterial, which, as described herein, may be an aluminum-scandium alloy.In some instances, the piston 58 may move in the direction 100 until thepiston 58 reaches the upper end 64 of the ram 74. As the piston 58 movesin the direction 100, the alloy can be pressurized and introduced intothe mold 52, specifically, into the mold cavity 62. The general flow ofthe alloy (i.e. the casting material) into the mold cavity 62 may berepresented by arrow 51 in FIG. 2. As the piston 58 moves in thedirection 100, the alloy fills the mold cavity 62, first from the abottom portion of the mold (near the upper end 64 of the ram 54) then tothe top of the mold (near the underside 78 of the cooling mold 56), asshown in FIG. 2. During casting, the pressure may be greater than about1 MPa (about 0.145 ksi). In some instances, the pressure may be betweenabout 10 and 100 MPa (about 1.45 and 14.5 ksi). The pressure may varydepending on, e.g., the geometry of the component being cast, which candetermine the shape of the mold cavity 62.

After the mold cavity 62 is filled with the alloy, the pressure may nolonger be applied. In some instances, the pressure may continue to beapplied after the mold cavity 62 is filled with the alloy for a periodof time until solidification of the alloy completes, which is describedin more detail below, and/or until a temperature of the compressorwheel, also referred to as the casting temperature, reaches about 300°C. In some instances, the period of time after casting during which thepressure may continue to be applied can be between about 1 and 10seconds, or between about 3 and 5 seconds.

After the mold cavity is substantially or entirely filled with thealuminum-scandium alloy casting material, solidification may take placeto form a solid component, such as a compressor wheel, also referred toas a casting. Solidification may occur when the mold cavity 62 is filledsuch that the aluminum-scandium alloy contacts (e.g. directly,physically contacts) the underside 78 of the cooling mold 56. In oneexample, solidification may begin when the casting material firstphysically contacts the underside 78 of the cooling mold 56. In otherinstances, solidification may begin when the casting material isintroduced into the mold cavity 62; however, most of the solidificationmay not take place until the casting material physically contacts theunderside 78 of the cooling mold 56 having coolant flowing therethrough.Unless specified, “contact” may refer to direct or physical contact, orthermal contact. Once the mold cavity 62 is filled and the alloycontacts the underside 78 of the cooling mold 56, heat may betransferred directly from the alloy to the mold, causing the alloy tocool and solidify to form a solid solution aluminum-scandium alloy.Thus, the cooling mold 56 can draw out the heat from the castingmaterial disposed within the mold cavity 62. The solid solutionaluminum-scandium alloy may also be referred to herein as solidsolution, a solid solution alloy, a solid solution casting, or the like.In the example of manufacturing a compressor wheel, cooling andsolidification may occur with a back-disk of the compressor wheel beingthe portion of the alloy in physical contact with the underside 78 ofthe cooling mold 56. Solidification during the casting method describedherein may preserve at least some of the amount of scandium within themolten alloy. In some examples, the disclosed solidification process maypreserve all or substantially all of the scandium in solid solutionwithin the casting material. For instance, where scandium makes up about0.2 wt % of the casting material when the material is first introducedinto the mold 52, scandium may still make up about 0.2 wt % of thecasting material after solidification with about 0.2 wt % of thescandium in solid solution in the solidified casting.

When solidification is complete, the mold 52 may be opened and thecompressor wheel can be removed from the mold cavity 62. If the mold 52is a retractable mold composed of multiple pieces, one or more pieces ofthe mold 52 may be removed to allow for removal of the compressor wheelfrom the mold 52. If the mold 52 is a single piece, the mold 52 may bebroken open to allow for removal of the compressor wheel.

After casting, once the compressor wheel is completely cooled, thecompressor wheel may be aged at a temperature, which may be referred toas an aging temperature, for a period of time. In some instances, theaging temperature may be between about 200° C. and 400° C. (e.g. about300° C.), and the aging time may be between about 1 and 24 hours (e.g.,between about 2 and 8 hours). Prior to aging the compressor wheel, thecompressor wheel may be pre-aged at a temperature for a period of time.The pre-aging temperature may be lower than the aging temperature, andthe pre-aging time may be longer than the aging time. For example, thepre-aging temperature and time may be about 150° C. and about 20 hours,respectively.

During the aging process, the precipitates 84 may be formed within thecasting. Specifically, Al₃Sc nanoscale or nanometer-sized precipitatesmay be formed. In some instances, the precipitates 84 may benon-uniformly or randomly distributed nanometer-sized precipitates 84,as shown in and discussed with respect to FIG. 3. In other instances,the precipitates 84 may be uniformly distributed in a portion, such asthe portion 82, or throughout the entire compressor wheel 46, 48.

The precipitates 84 may be formed as a result of preserving the amountof scandium in solid solution during solidification. For example, thefinal amount of scandium in solid solution after solidification may bebetween about 50 and 100% (e.g., about 80 or 90%), of the initial amountof scandium in the casting material before solidification. In someinstances, excess scandium can be initially provided in the castingmaterial to achieve a desired final amount of scandium in solid solutionduring and after solidification. For example, to achieve 0.2 wt %scandium in solid solution after solidification, an initial amount ofscandium greater than 0.2 wt % can be provided in the casting material.The amount of scandium initially provided in the casting material may beslightly greater than the desired final amount of scandium in solidsolution, or the amount of scandium initially in the casting materialmay be substantially greater than the desired final amount of scandium.For instance, to achieve a greater amount of scandium in solid solutionafter solidification, e.g., between about 1 and 5 wt % scandium, theamount of scandium initially in the casting material may besubstantially greater than between about 1 and 5 wt % scandium. On theother hand, to achieve a lesser amount of scandium in solid solutionafter solidification, e.g. about 0.2 wt % scandium, the amount ofscandium initially in the casting material may be slightly greater thanor substantially equal to about 0.2 wt % scandium. An initial amount ofscandium may be considered “slightly greater” than the final amount ifafter solidification there is between about 0% and 30% less scandium insolid solution than in the initial casting material beforesolidification. An initial amount of scandium may be considered“substantially greater” than the final amount if after solidificationthere is between about 30% and 95% less scandium in solid solution thanin the initial casting material before solidification. Furthermore, theamount of scandium initially in the casting material being slightlygreater than or substantially equal to the amount of scandium in solidsolution after solidification may be referred to herein as preserving a“substantial amount” of scandium, or another alloying element. In someinstances, the amount of scandium preserved can be all or substantiallyall of the scandium initially in the casting material.

As described herein, during solidification the alloy may be rapidlycooled, or quenched, within the mold cavity 62 by the cooling mold 56 topreserve at least some of the amount of scandium initially in thecasting material. The cooling rate applied to the alloy, which may be apredetermined cooling rate, may be sufficient to keep the scandium insolid solution in the casting material. For example, the cooling ratemay be between about 5° and 200° C./second (between about 41° F. and392° F./second). In one instance, the cooling rate may be about 100°C./second (about 212° F./second). In another instance, the cooling ratemay be about 40° C./second (about 104° F./second). The cooling rate mayalso be referred to herein as the “solidification rate” because thecooling rate may determine the length of time required to solidify themolten alloy within the mold 52 to form the compressor wheel. Rapidlycooling the alloy may cause the alloy to solidify directly from a giventemperature (e.g. a liquidus temperature), such that an amount of thescandium remains in solid solution in the casting material. For example,after solidification, scandium may make up about 0.2 wt % or more of thecasting material by rapidly cooling the alloy as described herein.Because scandium is preserved in solid solution in the casting material,during the aging process precipitates, specifically Al₃Scnanometer-sized precipitates, can be formed in the compressor wheelmaterial. For example, aging a compressor wheel cast according to themethod described herein at about 300° C. for about 2 hours can use theamount of scandium preserved in solid solution during solidification toproduce a plurality of Al₃Sc nanometer-sized precipitates. In someinstances, the amount of precipitates formed may be substantially thesame as the amount of scandium in the casting material before and/orafter solidification (e.g. about 0.2 wt %).

INDUSTRIAL APPLICABILITY

The above-described method and apparatus, while being described withrespect to a compressor wheel of a turbocharger in an internalcombustion engine, can be used generally in applications or industries(e.g. the automotive, gas turbine, or aerospace industries) involvingcomponents requiring high temperature and/or stress resistance.Additionally, the above-described method and apparatus can be used inapplications or industries requiring lightweight components.

The method and apparatus of the present disclosure can provide a viablealternative to titanium engine components such as compressor wheels. Inparticular, the present disclosure can enable effective utilization ofan alloying element such as scandium in the manufacture ofaluminum-scandium alloy compressor wheels. As described herein, duringmanufacturing the alloy can be rapidly cooled by the cooling mold 56configured to have a coolant flowing therethrough. This rapid coolingcan cause solidification of the alloy to form the compressor wheelcasting within the mold 52. The high cooling rate can preserve an amountof scandium in solid solution in the casting material, so that duringthe aging process, many nanometer-sized precipitates 84 (e.g. Al₃Scprecipitates) can be formed within the casting. For example, based onthe disclosed method, scandium may make up about 0.2 wt % or more of thecasting.

Due to the formation of many precipitates 84 within the casting, thecompressor wheel can have high temperature and/or stress properties toenable the aluminum-scandium alloy compressor wheel to withstand highoperating temperatures and stresses of an internal combustion engine.The formation of precipitates can prevent dislocation moving, and indoing so may increase the strength (e.g. the tensile strength and/or theyield strength) of the compressor wheel and decrease its malleability.In some instances, the aluminum-scandium alloy compressor wheel maywithstand operating temperatures of about 260-300° C., and in some casesgreater than about 300° C. Additionally, the formed compressor wheel mayhave a tensile strength of greater than or equal to about 250 MPa (about36.25 ksi) to meet the high stress requirements.

Pressurized casting can facilitate rapid cooling, which may help toentrap alloying elements in solid solution, and thus allow for theformation of precipitates 84 within the compressor wheel during thesubsequent aging process. During manufacturing, air gaps may existbetween one or more sides of the mold 52 and/or the underside 78 of thecooling mold 56. The pressurized casting process can reduce the size of,or altogether eliminate, the air gaps. Reduction in size and/orelimination of the air gaps can improve heat transfer between the alloycasting material and the molds 52, 56, which can facilitate rapidcooling of the casting material and the eventual formation during theaging process of nanometer-sized precipitates 84 therein. For example,pressure casting may increase the heat transfer coefficient by causingdirect physical contact between the compressor wheel being cast and theunderside 78 of the cooling mold 56, thereby improving heat transferfrom the compressor wheel to the cooling mold 56.

The pressure casting process described herein, which may includepreheating the mold 52 and/or ram 54, may also help to avoid prematuresolidification of the alloy casting material within the mold 52. Asdescribed herein, the casting material may not contact the underside 78of the cooling mold 56, and therefore may not be substantially cooledand solidified, until the mold cavity 62 is completely filled with thecasting material. Moreover, the mold 52 and/or ram 54 may be preheatedto help prevent early solidification of the casting material. Inaddition to the pressure casting process itself, the arrangement of themold 52, the cooling mold 56, and the ram 54 may allow for the moldcavity 62 to be filled with casting material from the bottom portion(i.e. near the upper end 64 of the ram 54) to the top portion (i.e. nearthe underside 78 of the cooling mold 56). Thus, the arrangement canprohibit contact between the casting material and the underside 78 ofthe cooling mold 56 until the mold cavity 62 is filled, thereby helpingto prevent premature solidification of the alloy casting material. Insome instances, pressure casting may also reduce porosity of the castingmaterial and thus eliminate other porosity reducing processes, such ashot isostatic processing, which may reduce the formation of nanometersized precipitates (e.g. Al₃Sc) and lose some or all strengtheningbenefits from alloying elements. Additionally, forming the mold 56 of athermally conductive alloy, such as copper or stainless steel, mayfurther facilitate heat transfer from the casting material to the mold56.

Using an aluminum-scandium alloy to form a turbocharger component suchas a compressor wheel may also allow for cost savings when compared toanother alloy, such as titanium. Additionally, an aluminum-scandiumalloy compressor wheel formed by the process described herein may belightweight, so as to reduce inertia of a turbocharger rotor, and thusincrease the turbocharger response and performance. Compared totitanium, aluminum alloys may be about 40% lighter than typical titaniumalloys. Therefore, providing an aluminum-scandium compressor wheel mayincrease engine transient response and reduce turbo-lag, while alsoimproving fuel efficiency during engine operation.

When the manufacturing method described herein is used to cast acompressor wheel or other component potentially having a complexgeometry, the mold 52 may be formed as a retractable, multiple-piecemold having a plurality of separable parts. These separable parts may bereferred to as segments, modules, or the like. Providing a retractablemold 52 may allow for the component to be easily removed from the mold52 after casting.

The compressor wheel of the present disclosure may be used in variousturbocharger systems. Although FIG. 1 shows a multiple stageturbocharger system, the compressor wheel of the present disclosure maybe used in a single stage turbocharger system. Furthermore, thecompressor wheel of the present disclosure may be used in a first stageof a compressor and/or in one or more later stage compressors. Moreover,although the disclosed method and apparatus may refer to compressorwheels, the method and apparatus may be applicable to components otherthan compressor wheels. For example, the disclosed method and apparatusmay be applicable to other turbocharger or internal combustion enginecomponents such as turbine wheels, cylinder heads, piston heads, or thelike. In addition, the method and apparatus may be applied to a varietyof other internal combustion engine components, or to components used invarious other industries and applications. Also, although the disclosedmethod and apparatus may refer to using scandium as an added material toform an aluminum-scandium alloy, the method and apparatus may beapplicable to added materials other than scandium, such as zirconium andtitanium. Furthermore, with regard to the mold 52, although the materialforming the mold 52 may be stainless steel, other alloys (e.g. copperalloy) may be used depending on the geometry of the component beingcast.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed apparatus andmethod for manufacturing a turbocharger component. Other embodimentswill be apparent to those skilled in the art from consideration of thespecification and practice of the disclosed apparatus and method. It isintended that the specification and examples be considered as exemplaryonly, with a true scope being indicated by the following claims andtheir equivalents.

What is claimed is:
 1. A method of manufacturing a turbochargercomponent for an internal combustion engine, the method comprising:introducing a material into a mold, wherein the material includes atleast one added alloying element; applying a pressure to the material;solidifying the material by cooling the material at a cooling rate,wherein the solidifying preserves an amount of the at least one addedalloying element in solid solution in the material; and formingprecipitates within the material by aging the material at an agingtemperature.
 2. The method of claim 1, wherein the cooling rate isbetween about 5° C. per second and 200° C. per second.
 3. The method ofclaim 1, wherein the material is an aluminum-scandium alloy.
 4. Themethod of claim 3, wherein the aluminum-scandium alloy includes about0.2 wt % scandium as the at least one added alloying element.
 5. Themethod of claim 1, wherein the pressure is applied to the materialduring and after the material is introduced into the mold and until thematerial solidifies.
 6. The method of claim 1, wherein the precipitatesare nanometer-sized precipitates of the at least one added alloyingelement randomly distributed throughout the turbocharger component. 7.The method of claim 1, wherein the mold includes a mold cavity, andwherein the solidifying occurs when the material fills the mold cavity.8. The method of claim 1, wherein during the solidifying the materialcontacts a cooling mold.
 9. The method of claim 8, wherein thesolidifying preserves a substantial amount of the at least one addedalloying element in solid solution in the material.
 10. The method ofclaim 8, wherein the mold includes a mold cavity, and wherein thematerial first contacts the cooling mold when the material fills themold cavity.
 11. The method of claim 1, wherein the material is firstintroduced into a bottom portion of the mold.
 12. The method of claim 1,wherein a coolant is introduced into a coolant passage of a cooling molddisposed above the mold.
 13. The method of claim 1, wherein theturbocharger component is a compressor wheel.
 14. A component for aturbocharger of an internal combustion engine, wherein the component ismanufactured by the method comprising: introducing a material into amold, wherein the material includes at least one added alloying element;applying a pressure to the material; solidifying the material by coolingthe material at a cooling rate, wherein the solidifying preserves anamount of the at least one added alloying element in solid solution inthe material; and forming precipitates within the material by aging thematerial at an aging temperature.
 15. The component of claim 14, whereinthe cooling rate is between about 5° C. per second and 200° C. persecond.
 16. The component of claim 14, wherein the material is analuminum-scandium alloy including about 0.2 wt % scandium as the atleast one added alloying element.
 17. The component of claim 14, whereinthe precipitates are uniformly distributed nanometer-sized precipitates.18. The component of claim 14, wherein the aging temperature is betweenabout 200° C. and 400° C.
 19. A component for an internal combustionengine, wherein the component comprises: an aluminum-scandium alloyhaving nanometer-sized precipitates, wherein the alloy includes about0.2 wt % scandium.
 20. The component of claim 19, wherein theprecipitates are randomly distributed throughout the component.